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Archives of an email list on the history of binoculars. - page 4 / 150

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  I'm a little disappointed that the Big Bino comparison did not include the Doctor 15/60 Nobilems. I've looked through several pairs, both Zeiss vintage and Doctors, and they have been uniformly excellent.

  One last parting spot for you telescope users. Today I recieved a Baader Planetarium Amici prism 90 degree diagonal (Alpine Astro $286). It's simply amazing. Using my C8 the diffraction pattern image of a point source is identical to a regular prism. I can't even see a diffraction spike. I will test it interferometrically tomorrow. In comparison I received a couple of weeks ago a Williams Optics 60 degree Amici diagonal (Anacortes $99) - after a 3 month back order. It was junk optically, I sent it back. With my C8 points sources looked like little double stars separated by 2 arc-seconds.       Randy Dewees

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Subject: Contrast Sharpness and Resolution

From: Kennyj2@___m

  In list *250  ( a  milestone worthy of note in itself in my view ) I was interested in our friend Arthur's comments on the relationship between Sharpness , Contrast and Resolution in response to the Astro -Bino article in April's Astronomy magazine by Phil Harrington . Not being able to shed any more light on the discussion due to lack of real understanding of this important and intriguing matter , I consulted my e -friend Ed Zarenski to ask if he could.  His reply was very interesting and with his permission I would like other members of the group to consider his opinions and comment where applicable .

  What follows is an extract from Ed's reply to me :

  "I think of Sharpness as the ability of the binocular to maintain a critically sharp image up to an increasing distance out from the center of the fov.  I believe most others also consider the term accordingly.  The adherance to strict curvature of the glass during manufacture, or a field flattener lens will improve Sharpness.

  Resolution, on the other hand, is the ability of the lens to bring the image to the finest point possible.  Think of resolution as the ability to produce a smaller Airy disk (strictly a function of aperture) while also keeping the diffraction fringes to a minimum.  If the fringes ( the rest of the pattern of rings around the Airy disk) is not minimized, the overlapping diffraction fringes make it much more difficult to resolve one fine pinpoint from the next.   Although most people simply consider the size of the aperture as the limiting factor for resolution, the quality of the chemical composition of the glass probably holds equal importance towards the limiting abilities.  I have seen better resolution in my 12x50 Pentax than in my 15x70 Oberwerk.

  Contrast is also a function of the chemical qualities of the glass, and not just the objectives but the prisms and eyepieces too.  Of course, coatings helps to improve contrast and therefore resolution.  But if the quality or the cut of the glass is low to begin with, then all the coatings and contrast in the world will not make the inferior lens perform better than the premium lens."

  Looking forward to any further comments -- Kenny .

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Subject: Optical & Film Supply

From: info@___ce.co.uk

>>7x50 porro prism models with the broad arrow MoD mark and the maker's imprint "Optical & Film Supply Company, NY, USA".<<

  I have seen a number of these in the UK and have a pair too, I think they are a early wartime delivery on a lease lend or hands across the sea. They seem to be based on early models MK1 etc

  There are a number of versions that I have seen – all made by "Optical & Film Supply Company, NY, USA" some have a small MOD arrow and some have much larger arrow

  I hope to put up a section with all the weird versions that I have found

  Hope everyone had a great time a the meeting in the US, Think it is time that the UK lot had another meeting – even if it is only at a pub.    Simon Gunning    www.oemspce.co.uk

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